This invention relates to a multi-band radio receiver and, more particularly, to an electronic tuning device for the multi-band receiver, in which the bands and the channels can be preset digitally.
Such radio receivers have been improved in various manners according to recent developments of electronic engineering and one such result is disclosed in Japanese Utility Model Application No. 11353/1975 in which a preset type multi-band receiver has a varactor diode tuner and a control therefor. The control comprises a channel selector switch means, a memory to be addressed by outputs of the channel selector switch, an up-down counter to be set by a manual pulse generator signal or a channel signal read out from the preset memory address and a digital-analog converter for converting an output of the counter into an analog signal which is supplied to the variable capacitor (Varactor) diode which forms a tuning circuit responsive to the analog signal for tuning the receiver to a desired signal in the preset channel.
In this case, the channel selector switch means is composed of a plurality of non-lock type switches.
The up-down counter is controlled by the output of the memory every time a channel selector signal from any one of the channel selector switches is detected. For a multi-band receiver, at least a band selector switch may be connected to the channel selector switches in series therewith.
In this case, however, since the output of the channel selector switch is different from that of the band selector switch in the standby state, that is, all of contacts of the channel selector switch are in off-state or low state, while the band selector switch is on except for instances of band selection between the adjacent bands. Therefore, in order to detect the outputs of both of the switches having different standby states, at least two kinds of circuits are necessary.
Further, although this type electronic tuner allows a relatively large number of preset data to be set reliably, the channel selection becomes relatively complicated because the memory supplies the information to the up-down counter according to the output of the channel selector switch. In other words, assuming, for example, that the channel is to be changed from channel number 3 in A band to channel number 3 in B band, that is, when the channel is changed from a certain channel number in one band to the same channel number in another band, it is necessary to operate the channel selector switch contact corresponding to channel 3 again after the band selector switch is switched from A to B.
In order to improve the tuner to eliminate these defects, a device such as shown in FIG. 1 has been proposed.
In FIG. 1, a pulse generator 1 has a pair of output terminals at one of which tuning pulses U/D are produced manually and at the other of which clock pulses KC are generated. The tuning pulses are either up count pulses U or down count pulses D, depending on the direction of the manual operation of the generator. The output terminals of the pulse generator 1 are connected to a binary up/down counter 2 which counts up or down the clock pulses KC depending on whether up or down are received from the pulse generator 1. A portion of an output of the U/D counter 2 is fed to a frequency indicator 3 which is, in this embodiment, a digital indicator.
The frequency indicator 3 provides an indication of the selected frequency by using some most significant bits of the parallel count output of the U/D counter 2. The output of the U/D counter 2 is also fed to an input of a pulse synthesizer 4 which, according to the output of the U/D counter, provides a serial pulse train including a predetermined number of pulses corresponding to the output of the U/D counter 2. The output of the pulse synthesizer 4 is fed to a low pass filter 5. The low pass filter 5 and the pulse synthesizer 4 constitute a digital-analog converter. A contact d of a first band selector switch 6 is connected to an output of the low pass filter 5. The band selector switch 6 has three contacts a, b and c, in this embodiment, which are connected to varactor diodes in tuning circuits for bands A, B and C, respectively.
A channel selector switch means 7 has a plurality of non-lock type switches 7a to 7e. One side of each of the switches 7a to 7e is connected to a common voltage source, +V.
A second band selector switch 8 is ganged with the band selector switch 6 and a contact arm d thereof is connected to the common connection of the switches 7a to 7e.
A random access read/write memory (RAM) system 9 comprises a channel memory 19 having inputs connected to the channel selector switches 7a to 7e, respectively, an address decoder 20 having inputs connected to outputs of the channel memory 19 and inputs connected to the contacts a, b, c of the band selector switch 8, and a RAM 21 having inputs connected to outputs of the address decoder 20 which latches the outputs of these switches so that, according to the outputs of the latter, the output of the up-down counter 2 is stored in an assigned address of the RAM and then read out therefrom and fed to the counter 2.
A controller circuit 10 has an input connected to one side of a preset switch 11 the other side of which is connected to the common connection of the channel selector switch means 7 and other band selector switch 8. The function of the control circuit 10 is to supply a load signal L to the U/D counter 2 when the preset switch 11 is off and an output is provided by any one of the channel selector switches 7a to 7e and to supply a write signal W to the RAM 21 when the preset switch 11 is on. The control circuit 10 may take various forms and comprises a controller, a band switch detector and a load pulse generator. The controller has an input connected to the preset switch 11 and a plurality of inputs connected to the other sides of the switches 7a to 7e. The band switch detector has its inputs connected to the contacts a, b and c of the switch 8, respectively. The load pulse generator 15 has an input connected to an output of the band switch detector 14. The controller provides a load signal output L and a write signal output W to the U/D counter and the RAM 9, respectively.
In manual operation when one operates the pulse generator 1 in one direction to generate the up-pulses U, for example, the latter is supplied to the U/D counter 2 causing it to count up the clock pulses KC from the pulse generator 1. The parallel outputs of the U/D counter 2 are coupled to the stages of the pulse synthesizer 4, respectively. Stages of the pulse synthesizer 4 are capable of providing different frequency signals, which may be produced by frequency-dividing an oscillation frequency signal by different divisors, respectively, according to the parallel outputs of the U/D counter 2. The synthesizer 4 synthesizes different frequency signals produced by the stages thereof according to the output of the U/D counter to produce a serial pulse train containing pulses the number of which corresponds to the output of the U/D counter. The serial pulse train from the pulse synthesizer 4 is fed to the low pass filter 5 to remove high frequency components thereof and produce a dc voltage signal corresponding to the output of the U/D counter 2. The dc voltage signal is fed to a varactor diode of one of tuning circuits (not shown) which was selected by the band selector switch 6 to obtain a tuning at the corresponding frequency.
A suitable number of most significant bits of the output of the U/D counter 2 are fed to the frequency indicator 3 to visually and digitally indicate the frequency being received.
In preset operation, it is assumed that a desired channel in a desired band has been selected in the manner described above.
By turning the preset switch 11 on and then turning any selected one of the channel selector switches 7a to 7e on, a write signal W is generated in the control circuit 10 and fed to the RAM 21, so that the count output of the U/D counter 2, i.e., a digital signal corresponding to the tuned frequency being received, can be stored in an address of the RAM 21 assigned by the band selector switch 8, and the selected one of the switches 7a to 7e being on. Thus, certain channels in certain bands can be preset in the RAM, individually.
A certain channel in a certain band which is thus preset is selected by selecting the contact of the band selector switch and the channel selector switch corresponding thereto. Since, at the selection of the band selector contact and the band selector switch the preset switch 11 is off, the control circuit 10 supplies the band signal L to the U/D counter. As a result, the parallel readout signal from the RAM 21 which, receives the outputs from the band selector switch 8 and the channel selector switch 7 as an address to be readout, is fed to the U/D counter 2.
The U/D counter 2 provides an output, as mentioned before, which is fed to the pulse synthesizer 4, in the same manner as in the manual operation.
The change in channel in the same band can be performed by merely selecting a desired channel selective switch to be on.
When only the band is to be changed while the channel number is fixed, it is sufficient to switch the contact of the band selector switch 8 to a desired band.
As for the pulse generator, it should be of a type which is simple in construction and manually controllable. In order to satisfy these requirements, the pulse generator may be mechanical and comprise a rotary disc supported by a shaft having a free end equipped with a knob member. The disc has a plurality of equally spaced through-holes or slits arranged along the peripheral portion thereof. At least one light emitting element is disposed on one side of the disc and at least a light receiving element is arranged on the other side of the disc so that the light emitted from the light emitting element can be received by the light receiving element through the slits. By turning the knob in one or the other direction, the light to be received by the light receiving element becomes intermittent, so that the latter element provides a series of pulses the number of which corresponds to the angle of the rotation of the disc. This pulse generator is successive in one sense. However, the output pulse waveform of the light receiving element depends upon the rotation speed of the knob and is not rectangular but sinusoidal, causing the digital handling of the output pulse to be difficult. Furthermore, although the number of pulse outputs should be large enough to obtain correspondencies to a number of data, it is difficult to increase the number of the slits due to the available space. Further, due to undesirable reflection and/or leakage of the light, the S/N ratio is degraded causing the channel selection to be unstable.